Add lightweight accessible code-block controls to both editions

[trsdn]

Goal

Add useful preview code-block interaction independently of whether Lite Prism or Full highlight.js performs highlighting.

Requirements

• Show a language label plus Copy, wrap/no-wrap, and optional line-number controls.
• Keep controls unobtrusive but keyboard reachable; announce copy success without shifting layout.
• Copy exact Markdown code-fence content rather than highlighted HTML.
• Use a narrow platform clipboard path without broad WebKit permissions or a UI dependency.
• Preserve horizontal scrolling, selection, accessibility, themes, live-preview performance, and large-block performance.
• Hide interactive controls in print output while retaining readable code formatting.
• Unknown or failed highlighting must still receive functional controls.